Added help on the regexp search syntax.
Added help on the regexp search syntax.

tiborsimko/invenio-records,inveniosoftware/invenio-search,inveniosoftware/invenio-records,inveniosoftware/invenio-records,inveniosoftware/invenio-search,tiborsimko/invenio-records,tiborsimko/invenio-search,tiborsimko/invenio-search